Caption: Scientist examining an agarose electrophoresis gel used to prepare a DNA sequencing autoradiogram. The sample of DNA is marked with a radioactive tag in preparation for sequencing. During electrophoresis the DNA fragments move along the gel, separating according to size. The DNA banding pattern, which appears pink under ultraviolet light, is preserved by applying radiographic film to the gel. The resulting pattern of bands, the base sequence of a particular section of DNA, is known as a DNA sequencing autoradiogram. The most important sections of DNA, those which encode specific proteins, are known as genes.